Robert Plomin is an Americanpsychologist best known for his work in twin studies and behavior genetics. Plomin has made two of the most important discoveries in that field. First, he has shown the importance of non-shared environment, a term that he coined to refer to the environmental reasons why children growing up in the same family are so different. Second, he has shown that many environmental measures in psychology show genetic influence and that genetic factors can mediate associations between environmental measures and developmental outcomes.

Plomin is currently conducting the Twins Early Development Study (TEDS) of all twins born in England from 1994 to 1996, focusing on developmental delays in early childhood and their association with behavioural problems.